The catalysts utilized in conventional gas oil fluid catalytic cracking (FCC) operations are tailored and prepared with less than 20 wt % zeolite for use other than in high carbon and metals depositions reduced crude cracking operations. The fact that these known catalysts may be used to crack residual oils and reduced crudes in a marginal short time operation does not mean they are economically suitable for processing liquid carbo-metallic oil contributing materials such as asphaltenes, polynuclear aromatics, polar molecules, naphthenes and porphyrins found in the residue of vacuum distillation and boiling above 1025.degree. F. or more usually above 1050.degree. F. Generally, a conventional gas oil FCC system employs a catalyst of relatively low crystalline zeolite content less than 20 wt % (10-15 wt %) which has a relatively low hydrothermal stability due to a low silica to alumina ratio zeolite; comprises a high cerium to lanthanum ratio exchanged crystalline zeolite dispersed in a matrix material of low pore volume usually not above about 0.22 cc/gm; and comprises a pore size opening of less than 500 angstroms. Generally, the matrix is merely a binder material of little or no acidic cracking activity.
The processing of gas oils (atmospheric and vacuum) and boiling below about 1025.degree. F. with crystalline zeolites containing cracking catalysts has been available to the petroleum refiner since the early 60's and used considerably in the 70's. Generally such gas oil feeds are relatively low in metal contaminants and Conradson carbon value because of the feed purity sources selected. In addition, high sulfur or sour crudes and those comprising high levels of metal contaminants were not used in FCC operation in the absence of severe treating processes to remove or substantially reduce these undesired components. Such processes include hydrogenation, propane deasphalting, coking, hydrocracking, visbreaking and vacuum distillation. These processes are expensive and considerably reduce the volume of the crude oil upgraded to transportation fuels.
The catalysts developed for gas oil FCC processing have been developed to provide a high conversion and high selectivity to particularly gasoline boiling range products and light cycle oils since higher boiling product material is normally recycled to the cracking operation. In this gas oil processing environment, the deposition of metals is relatively low because of feed composition as well as the Conradson carbon level being generally below about 1 wt % and more usually such Conradson carbon deposition is within the range of 0.1-0.2 wt %. The feeds used in such gas oil operations are readily vaporized at the cracking reaction conditions and thus deposition of large amounts of liquids on the catalyst is minimized if not avoided. In FCC gas oil cracking operations, diffusion of the gas oil feed in the fluid particle size catalyst is not a major problem and pore blockage by excessive metal deposition by high boiling liquid hydrocarbons and by high coke deposition is not encountered as a major problem in the operating environment. Since deposition of undesired metal components and carbon is normally of a low order of magnitude there has been less need to provide a matrix material particularly designed or tailored to accumulate metal to the exclusion of substantially disturbing the catalyst cracking activity. Furthermore, and much more importantly, there has been no recognition by others of the need to particularly immobilize vanadia (vanadium pentoxide) because the level of depositon of vanadia encountered in gas oil cracking did not trigger recognition of particle sintering and coalescence due to liquefaction of this material at regeneration temperature conditions in the range of 1200.degree. to 1600.degree. F.
In contrast to the gas oil FCC operation as it is now known today, a reduced crude conversion operation processing much poorer quality feeds which have not been subjected to vacuum distillation, propane deasphalting and other contaminant removal processes as by hydrogenation, contain high levels of metal contaminants, sulfur and nitrogen compounds and a high Conradson carbon value. This high boiling dirty feed which we have chosen to define as carbo-metallic feed, composition characterization is particularly representative by much of the very poor qualtity feeds available to the refiner today.
The use of a conventional low zeolite content, less than 20 wt % zeolite containing FCC conversion catalyst as known today in a reduced crude conversion process leads to rapid catalyst deactivation by metals and high carbon deposits which can be corrected only by using very high catalyst replacement rates contributing to a highly unattractive economic operation. The rapid deactivation of the low zeolite containing catalyst is due to a rapid loss in zeolite activity and selectivity by metals deposition and relatively low hydrothermal stability for handling high levels of carbon deposition during regeneration thereof. Our studies have shown that high temperature regeneration in the presence of steam and especially vanadium and oxygen, rapidly destroys the activity of the zeolite cracking component of the catalyst and the zeolite cracking component of the catalyst and this condition is aggravated by using low silica-alumina ratio, higher sodium containing zeolites in conjunction with high metals deposition comprising vanadium, sodium and nickel, leading to rapid zeolite cracking activity neutralization. In addition the activity of the catalyst is affected by the large amount of heavy high boiling hydrocarbons in reduced crudes that are not vaporized and rapidly coat the catalyst particles with tacky liquid material also causing particle coalescence and agglomeration because of materials such as asphaltenes in the feed. Furthermore, the sorbed heavy hydrocarbons contribute to pore blockage, both in the matrix, and especially zeolite pores, and aggravate diffusion problems because of low pore volume, and effect acid site neutralization by adsorption of basic nitrogen compounds in the high boiling reduced crude feed.
The problems above reported with respect to cracking activity, acidity, hydrothermal stability, diffusion and pore blockage, sodium content of the zeolite, acid site neutralization, metals accumulation and vanadia immobilization are reduced or circumvented in substantial measure by employing the special catalyst compositions of the present invention for use in a Reduced Crude Conversion Process.